1. Field of the Invention
The present invention relates generally to UV-scattering inorganic/polymer composite particles and a method for preparing the same.
2. Description of the Related Arts
Recently, we have been worried about destruction of ozone layer and thereby increase of harmful ultraviolet (UV) to seriously affect on ecosystem. Particularly, cosmetic field or coating or painting field are concerned on this increase of harmful UV. That is, because UV penetrated into the skin causes melanoma or erythema, cosmetic field has a task to develop cosmetics for blocking UV.
Conventionally, UV-absorbing materials and UV-scattering materials have been formulated in separate or in combination, in order to block a contact of UV and the skin. UV-absorbing materials are compounds having π-conjugate molecular structure and having UV-blocking efficiency by absorbing UV and then by radiating transformed secondary energy. But, these compounds have defect to limit the amount used due to their toxic characters.
Further, as UV-scattering materials, extreme fine titanium dioxide and zinc oxide have been representatively employed. But, these inorganic UV-scattering particles have high density and high polarity to cause phase separation such as sedimentation and coagulation in organic mixture. Particularly, in UV-blocking cosmetics, this phase separation may depreciate UV-blocking efficiency and rapidly down stability of formulation. Because 15˜30 nm of inorganic particles have high surface polarity and density, they cannot be dispersed stably in hydrophobic monomer phase of suspension polymerization. Additionally, when large quantity of inorganic particles is applied on the skin, it causes whitening phenomenon wherein the skin seems white or blue. This whitening phenomenon may depreciate the value of cosmetic goods to cause people to shun use of UV-blocking cosmetics. And, there is defect such as sticky feeling by using nano-sized inorganic particles.
Therefore, in order to solve the above problems caused by inorganic scattering materials, various efforts have been made. For examples, in order to improve stability in formulation, inorganic particles may be coated with organic materials or surfactant and formulation property may be controlled. Concretely, U.S. Pat. Nos. 6,123,927 and 5,980,871 disclosed a method for improving UV-scattering efficiency and formulation stability by controlling component ratio and particle size. But, though initial dispersion is improved, it is impossible to overcome low compatibility with other components in formulation and thereby impossible to improve long-term stability and temperature stability. Korean Patent No. 275022 expected synergistic effect by encapsulating titanium dioxide and transformed micro-hollow sphere with polymer micro-sphere. But, it cannot solve the defects caused by titanium dioxide.
Under this circumstance, in order to solve said problems, the present inventors have conducted extensive studies on novel material having intrinsic UV-scattering efficiency and without said defects caused by inorganic particles. As a result thereof, we found that inorganic/polymer composite particles obtained by suspension polymerization of monomer and inorganic particles exhibit improved UV-scattering efficiency and good dispersion stability. In the present method, inorganic particles are employed after surface treatment with organic material in order to increase dispersivity in monomer.